The present invention relates to an evaporation apparatus for forming a metal membrane on a film substrate.
In recent years, an evaporation apparatus has been widely used to evaporate a metal membrane over a magnetic recording tape or a film capacitor or the like.
An example of a conventional evaporation apparatus will be described below with reference to FIG. 3. The apparatus comprises a film substrate 1 to which an evaporated material is attached; an evaporation material 2; a vacuum evaporation means 13, provided on a container 3 for containing the evaporation material 2, consisting of such means as resistance heating, high frequency induction heating, or an electron beam for melting and evaporating the evaporation material 2; a drum 4 rotating in opposition to the vacuum evaporation means and containing cooling liquid circulating so as to cool the surface of the film substrate 1 on which the evaporated material is being deposited; a supply roller 5 for supplying the film substrate 1 to the drum 4; an ungrounded winding roller 6 for winding up the evaporated material-deposited film substrate 1, the surface of which contacts the film substrate 1 and is covered with an insulating tape or an insulating coating material such as polytetrafluoroethylene resin; ungrounded free roller 7a, for assisting the winding or travel of the film substrate 1, the surface of which contacts the film substrate 1 and is covered with an insulating tape or an insulating coating material such as polytetrafluoroethylene resin; an ungrounded free roller 7b for assisting the winding or travel of the film substrate 1 and in conductive contact with the surface of the film substrate 1 on which the evaporated material has been deposited; a vacuum chamber 8; a vacuum pump 9 for evacuating the interior of the vacuum chamber 8; a DC power source for applying, through the free roller 7b, a DC voltage to the evaporated material-deposited film 1.
The operation of the apparatus of the above construction is described below.
The interior of the vacuum chamber 8 is evacuated to a vacuum degree of approximately 5.times.10.sup.-5 Torr by the vacuum pump 9 such as a rotary pump, oil diffusion pump, or a cryopump. Then, the supply roller 5, the drum 4, and the winding roller 6 are driven. The film substrate 1 travels in order from the supply roller 5, over the free roller 7a, the drum 4, the free roller 7b, and the free roller 7a, and finally is wound around the winding roller 6. The evaporation material 2 is melted and evaporated by the vacuum evaporation means consisting of such means as resistance heating, high frequency induction heating, or electron beam. Evaporated particles splash and are deposited on the surface of the film substrate 1 being fed along the surface of the drum 4 to form a metal membrane on the surface of the film substrate 1. At this time, the DC power source 10 applies a positive or a negative voltage to the evaporated material-deposited film substrate 1 through the free roller 7b so as to generate a potential difference between the film substrate 1 and the drum 4. As a result, the film substrate 1 which has been brought into close contact with the drum 4 is cooled because the drum 4 contains cooling liquid which is circulating. The film substrate 1 then travels to the free roller 7a and is wound around the winding roller 6.
However, the above-described construction does not allow the evaporated material to adhere to the film substrate 1 with a great strength. In order to overcome this disadvantage, as a pre-treatment, it is necessary to remove water and impurities by means of annealing or impurities by means of plasma treatment and form irregularities on the surface of the film substrate 1. Thus, the manufacturing operation requires much time and labor, also requiring the provision of equipment for the pre-treatment if necessary. In addition, with the increase of the quantity of ions contained in splashed particles of the evaporation material 2 which has melted and been evaporated by the evaporation means, ions increasingly collide with the film substrate 1 opposite to the evaporation means. As a result, the film is thermally deformed by ion energy, namely, stretched, contracted or melted.